Gibbs
Gibbs can be extremely charming in an understated way and has a dry sense of humor. He is unforgiving of his or his colleagues' mistakes and demands high standards of himself and his team.
He is building a boat in his basement by hand, with no power tools. According to the series, he did so after each time he has been divorced. It is also stated that he destroyed each one after it was done. It is also hinted that he names the boats after women he is involved with, and when the relationship ends, so does the boat.
He has a coffee addiction and even has a personal rule about it: "Rule 23, never mess with a Marine's coffee if you want to live". He also appears to be farsighted, as early episodes of the series reveal that he has difficulty reading fine print, though he refuses to wear reading glasses. Although in some episodes he puts on director Shepard's glasses when the two of them are in her office and he has to read something.
Gibbs is usually portrayed as a complex man of mystery and intrigue. He likes to use his marine training to give him an advantage over other people, such as when he silently appears behind people.
When it was revealed that his wife and daughter were murdered by a drug runner, Ducky casually states that they can close the book on the drug runner's disappearance, because there is no way that Jethro would have allowed the man to remain alive. In the same episode it was revealed that Jethro gained access to the case file, crossed the border into Mexico, and killed the man with a sniper rifle.
Whenever he needs to have a private talk with someone, usually FBI Special Agent Tobias Fornell, but also occasionally Ziva and others with whom Gibbs confides, he takes them to his "Conference Room," which is basically just the main elevator of NCIS headquarters with the emergency brake pulled.
Gibbs has displayed an uncanny awareness of his co-workers activities. An oft-repeated scene has Gibbs walking in on his team-members having an off-topic conversation: even though they immediately break off to focus on the case at hand, Gibbs drops a remark later on referring back to the earlier conversation. In "Escaped" 4x02, Tony attempts to replicate this action by "listening in" on their conversation with a cell phone and an opened line. However, Gibbs trumps him after his attempt.
His taste in "pop culture" is rarely discussed; however, in the series pilot, he is revealed to have seen the movie Air Force One with Harrison Ford. A recurring theme is how out of step Gibbs is with popular culture.
In Season 4 Gibbs has been shown to be able to speak Russian as he speaks to the suspect in Russian.
He also has a photograph of a tombstone on the wall in his cubicle. Presumably it is his first wife's or his daughter's.
Information from Wikipedia, image I found on Photobucket
